Effect of the irradiance distribution from light curing units on the local micro-hardness of the surface of dental resins.

Haenel, T ; Hausnerová, B ; et al.

In: Dental materials : official publication of the Academy of Dental Materials, Jg. 31 (2015-02-01), Heft 2, S. 93-104

academicJournal

Objective: An inhomogeneous irradiance distribution from a light-curing unit (LCU) can locally cause inhomogeneous curing with locally inadequately cured and/or over-cured areas causing e.g. monomer elution or internal shrinkage stresses, and thus reduce the lifetime of dental resin based composite (RBC) restorations. The aim of the study is to determine both the irradiance distribution of two light curing units (LCUs) and its influence on the local mechanical properties of a RBC.

Methods: Specimens of Arabesk TOP OA2 were irradiated for 5, 20, and 80s using a Bluephase® 20i LCU in the Low mode (666mW/cm(2)), in the Turbo mode (2222mW/cm(2)) and a Celalux® 2 (1264mW/cm(2)). The degree of conversion (DC) was determined with an ATR-FTIR. The Knoop micro-hardness (average of five specimens) was measured on the specimen surface after 24h of dark and dry storage at room temperature.

Results: The irradiance distribution affected the hardness distribution across the surface of the specimens. The hardness distribution corresponded well to the inhomogeneous irradiance distributions of the LCU. The highest reaction rates occurred after approximately 2s light exposure. A DC of 40% was reached after 3.6 or 5.7s, depending on the LCU. The inhomogeneous hardness distribution was still evident after 80s of light exposure.

Significance: The irradiance distribution from a LCU is reflected in the hardness distribution across the surface. Irradiance level of the LCU and light exposure time do not affect the pattern of the hardness distribution--only the hardness level. In areas of low irradiation this may result in inadequate resin polymerization, poor physical properties, and hence premature failure of the restorations as they are usually much smaller than the investigated specimens. It has to be stressed that inhomogeneous does not necessarily mean poor if in all areas of the restoration enough light intensity is introduced to achieve a high degree of cure.

Titel:	Effect of the irradiance distribution from light curing units on the local micro-hardness of the surface of dental resins.
Autor/in / Beteiligte Person:	Haenel, T ; Hausnerová, B ; Steinhaus, J ; Price, RB ; Sullivan, B ; Moeginger, B
Zeitschrift:	Dental materials : official publication of the Academy of Dental Materials, Jg. 31 (2015-02-01), Heft 2, S. 93-104
Veröffentlichung:	1998- : Kidlington, Oxford, UK : Elsevier Science ; <i>Original Publication</i>: Copenhagen : Munksgaard, c1985-, 2015
Medientyp:	academicJournal
ISSN:	1879-0097 (electronic)
DOI:	10.1016/j.dental.2014.11.003
Schlagwort:	Hardness Materials Testing Spectroscopy, Fourier Transform Infrared Surface Properties Time Factors Curing Lights, Dental Light Resins, Synthetic chemistry Scattering, Radiation
Sonstiges:	Nachgewiesen in: MEDLINE Sprachen: English Publication Type: Journal Article; Research Support, Non-U.S. Gov't Language: English [Dent Mater] 2015 Feb; Vol. 31 (2), pp. 93-104. <i>Date of Electronic Publication: </i>2014 Dec 05. MeSH Terms: Curing Lights, Dental* ; Light* ; Scattering, Radiation* ; Resins, Synthetic / *chemistry ; Hardness ; Materials Testing ; Spectroscopy, Fourier Transform Infrared ; Surface Properties ; Time Factors Contributed Indexing: Keywords: Degree of conversion; Dental resin; FTIR; Hardness mapping; Irradiance distribution; Knoop micro-hardness; Light curing units Substance Nomenclature: 0 (Resins, Synthetic) Entry Date(s): Date Created: 20141209 Date Completed: 20161213 Latest Revision: 20220409 Update Code: 20240513

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